Lighting transformer



June 7, 1949. P, BERGER Y 2,472,140

LIGHTING TRANSFORMER Filed Aug. 31, 1945 2C JNVENTOR.

2 PAUL BERGER Y/mofzlmzwr Patenteci June 7, 1949 LIGHTING TRANSFORMER,

Paul Berger, Chicago, Ill., assigner, by mesne assgnments, of one-halfto Hirsch Epstein and one-half to Louis R. Duman, both of Chicago, Ill.

Application August 31, 1945, Serial No. 613,779

4 Claims.

This invention relates to a transformer and more particularly to atransformer for operating a plurality of hot cathode glow-dischargelamps, such as fluorescent tube lamps.

In order to improve the power factor of lighting circuits of fluorescenttube lamps it has been customary to operate the tubes in pairs off of asingle transformer. There is provided an operating transformer having apair of secondaries, one for each fluorescent tube. A condenser isprovided in series with only one of the tubes to cause that tube to drawa leading current. This leading current compensates for the laggingcurrent taken by the other tube, whereby the power factor of theI loadof the two tubes is improved.

Fluorescent tubes of the hot cathode type are started by providing atemporary series connection between the filaments at the opposite endsof the tube. A current of sufficient magnitude to heat the laments iscaused to flow through them. After a time interval adequate to allow thefilaments to reach a temperature sufficient for the glow discharge arcto form, the series circuit between the filaments is automaticallyinterrupted by a starter provided in the circuit, as is known in theart. In starting two lamps of the above mentioned character, which areconnected to be operated from a single circuit, it has been found thatthe condenser which is in series with the filaments of only one of thelamps reduces the current flow to that lamp to a degree which isundesirable for satisfactory starting in many instances. In addition, inmany instances there is sufficient reactance between the secondary coilsof the transformer so that a reduction of the current flowing in thesecondary which is in series with the condenser results in an increasein the current owing in the other secondary which is connected to theother lamp. Thus the condenser not only diminishes, to an undesirabledegree, the amount of current flowing in the starting circuit of one ofthe lamps but likewise also frequently increases, to an undesirabledegree, the amount of current owing to the other lamp. It has heretoforebeen proposed to remedy this condition by providing an additionalinductance outside of the transformer, which additional inductance istemporarily connected in circuit with the condenser to reduce thereactance of the associated circuit during starting. This substantiallyincreases the expense of the equipment required for each pair ofuorescent lamps.

It is one of the objects of the present invention tor provide a circuitarrangement whereby the Voltage of and consequent current in thestarting circuit of the lamp having the leading power factor isincreased without substantially increasing the total cost of theequipment used. This is accomplished, in the preferred embodiment of thepresent invention, by providing an auxiliary coil on the transformerwhich supplies the power to the pair of fluorescent lights. Thisauxiliary coil is arranged to be treaded by the magnetic flux thattreads at least one of the secondary windings, or the primary winding.During starting the auxiliary coil is connected in series with thatsecondary coil which supplies current to the leading lamp and with thevoltages of the series connected coilsv cumulative. This auxiliary coilcompensates for the reactance of the condenser in that circuit and, inaddition, increases the voltage of that circuit. This auxiliary coil isdisconnected from the circuit upon operation of the starter to interruptthe series connection between the heating coils of the two cathodes ofthe lamp. By this arrangement I have found that the starting current inthe leading tube, which previously was too low, is increased, and thestarting current i-n the lagging tube, which previously was too high, isdecreased. Thus the starting currents in both tubes tendv to equalizeand therefore the circuit, including the transformer, may be designed sothat the starting currents in both the leading and the lagging tubes maybe brought to the desirable values set .by the Electrical TestingLaboratories, Inc.

The attainment of the above and further objects of the present inventionwill be apparent from the following specication taken in conjunctionwith the accompanying drawing forming a part thereof.

In the drawing:

Figure 1 is a diagrammatic view of a transformer embodying the presentinvention, connected in circuit with two fluorescent lighting tubes; and

Figure 2- illustrates an alternate circuit.

At I and 2 there has been shown a pair of hot cathode glow dischargefluorescent tubes or lamps of conventional construction having heatinglaments la and I b and 2a and `2b. The two lamps are adapted to beenergized by a transformer I0. The transformer I 0 includes asubstantially closed magnetic circuit having a pair of series connectedprimaries lI-ll connected across the alternating current power line l2.The transformer has a pair of series connected secondary coils l3-I3 onthe same core structure lll,l which coils I3' are connected at one endto one side of the line and at the other end in series with thefilaments 2a- 2b and with a starter 2c, thence to the other side of theline. This constitutes the coil I3 part of an auto-transformer. This isthe circuit for the tube 2, which is the lagging tube, and is aconventional circuit. The starter 2c comprises merely an evacuated tubehaving a pair of contacts spaced apart in a gaseous atmosphere such adistance that a discharge takes place when subjected to the highstarting voltage, so that the resulting arc sufficiently heats one ofthe contacts, which is a thermal element, to cause a short circuitwithin the starter 2c, thereby establishing a series circuit between thelaments 2a and 2b. By the time the contacts in the starter 2c havesuciently cooled to separate from one another the filaments rc---Zb haveheated sumciently so that upon separation of the contacts of the starterthe resulting voltage causes an arc to be established between thecathodes at opposite ends of the tube 2.

The transformer Eil also has another pair of series connected secondarywindings Iii- I6 similar to the windings i3 and preferably of the samenumber of turns. One end of a winding I6 is connected to one side of theline I2 and the other end of the other winding IS is connected in serieswith a condenser l'l, the filament Ib, thence through a pair of startingcoils I8 connected in series and located upon the magnetic structureIii, thence in series through a starter Ic, similar to the starter 2c,thence in series with the lament la to the opposite side of the line.The coil i5, like the coil I3, acts as part of an autotransforrner. Thestarting circuit through the leading tube I includes the starting coilI8 which compensates for the reactance of the condenser i'I and, beingon the iron core of the transformer I0, increases the voltage of thestarting circuit of the tube I over what would have prevailed if thecoil it had been omitted. This thereby increases the current flowingthrough the starting circuit of the filaments Ia-Ib and at the same timereduces the current through the starting circuit of the laments Zac-2bover what would have been the current ow had the coils I8 been omitted.After the starting operation has been completed and the starter switchIc opens its circuit and the current flows across the space between thefilaments Ia-I b, the coil I6 is open circuited and therefore performsno function.

For the salie of compaotness the condenser Il is mounted in the samecase in which the transformer is located, so that together theyconstitute one unit with the necessary connections between the condenserand the secondary IE, contained within the casing. Therefore only sixleads need extend from the casing.

An analysis of the circuit illustrated shows that during the startingoperation the coil I3 acts not only as an inductance but also as anautotransformer. Because of this fact the coil I 8 may be made ofappreciably fewer turns than would be necessary if the coil I8 wereoutside of the magnetic circuit of the core I0. In one constructionwherein the total primary windings Il had 2200 turns and there were 1700turns in the secondaries I3 and 1700 turns in the secondaries I5, it wasfound that 250 turns for the auxiliary winding i8 were adequate. Thecoils I8 were therefore so narrow as not substantially to increase thespace between the coils II-I6 compared with the space between the coilsI I-I3.

During starting the number of turns of secondary winding that producesan auto-transformer effect for supplying current to the lamp I is equalto the sum of the turns on the coils I6 and i8. When the coils I8 arelocated in the proximity of the coils I6 the coils I3 have a smalleffect upon the flux through the coils I3. If the coils I8 arephysically located on the core I0 adjacent the secondary coils of thelagging lamp, instead of adjacent the secondary coils of the leadinglamp, then the effect of the coils I8 in reducing the amount of currentflowing through the lagging lamp circuit during starting is accentuatedwithout altering the cumulative effect of the series connected coils,including the auxiliary coil I8, insofar as concerns the starting actionof the leading hot cathode glow discharge tube.

In those instances where it is found that the starting current for thelagging lamp 2 is too great, the compensating coils I8 in series withthe leading lamp are located adjacent the secondaries that supply thecurrent to the lagging tube in order to reduce the starting current inthe laments 2a-2b. This is illustrated in Figure 2 wherein theconnections from the coils I3-I6 have been interchanged over that shownin Figure 1.

From the above description it is apparent that there is provided atransformer and a circuit therefor for providing a sufficient startingcurrent for leading and lagging hot cathode glow discharge tubes andwherein the difference in starting current taken by the two tubes is sosubstantially reduced that the current values taken by each tube arewithin the maximum and minimum starting currents established byElectrical Testing Laboratories, Inc.

ln compliance with the requirements of the patent statutes have hereshown and described a few preferred embodiments of my invention. Itishowever, to be understood that the invention is not limited to theprecise construction here shown, the same being merely illustrative ofthe principles of the invention.

What I consider new and desire to secure by Letters Patent is:

l.. In combination with a pair of hot cathode glow discharge tubes eachhaving cathode heating means at opposite ends thereof and each having astarting switch. for connecting its heating means in series to elfectstarting of the tube and then opening the series connection, atransformer having a primary and a pair of secondaries, each secondarybeing connected in circuit to one of said tubes, a condensive reactancein circuit with one of the secondaries for power factor compensationwhereby one of said tubes takes a leading current and the other tube alagging current, and a starting coil in series connection with thestarting switch of the tube taking the leading current, said startingcoil and its series connected switch being connected in series with andbetween the cathode heating means at the ends of the tube taking theleading current, said starting coil being magnetically coupled with theprimary and with its voltage additive to the voltage of the secondary incircuit with the leading tube when the starting coil is connected incircuit by its associated starting switch, said starting coil beinglocated between the primary and one of said two pairs of secondaries.

2. in combination with a pair of hot cathode glow discharge tubes eachhaving cathode heating filaments at opposite ends thereof and eachhaving a starting switch for connecting its filaments in series toeffect starting of the tube and then opening the series connection, atransformer having a primary and a pair of scondaries each of whichsecondaries is connected to the primary to form an auto transformer,each secondary being connected in circuit across the cathodes of one ofsaid tubes, a condensive reactance in series with one of the secondariesfor power factor compensation whereby one of said tubes takes a leadingcurrent and the other tube a lagging current, and means for increasingthe voltage across the leading tube during starting to compensate forthe Voltage drop through the condensive reactance, said means comprisinga starting coil in series connection with the starting switch of thetube taking the leading current, said starting coil and its seriesconnected switch being connected in series with and between the cathodeheating means at the ends of the tube taking the leading current, saidstarting coil being magnetically coupled with the primary and with itsvoltage additive to the voltage of the secondary in circuit with theleading tube when the starting coil is connected in circuit by itsassociated starting switch, said starting switch in its open positionopen circuiting the starting coil, said starting coil being locatedbetween the primary and one of said two pairs of secondaries.

3. A transformer for supplying electrically displaced currents foroperating a plurality of separately operable hot cathode tubes, saidtransformer having an elongated magnetic core, a primary coil positionedon said core intermediate the ends thereof, a pair of secondary coilspositioned on the core on opposite si-des of the primary coil, each ofsaid secondaries being connected to the primary toform an autotransformer, separate load leads extending from the secondaries, astarting coil on said core adjacent to the primary coil and locatedbetween it and one of the secondary coils, a casing for saidtransformer, separate leads for the starting coil extending out of thecasing, starter switch means connected to one of the leads of thestarting coil for establishing switching connections for con- 6 nectingand disconnecting said starting coil in circuit with one of thesecondary coils, and a condenser in said casing, said condenser beingconnected in series with the last mentioned secondary coil.

4. A transformer for supplying electrically displaced currents foroperating a plurality of separately operable hot cathode tubes, saidtransformer having an elongated magnetic core, a primary coil positionedon said core intermediate the ends thereof, a pair of secondary coilspositioned on the core on opposite sides of the primary coil, each ofsaid secondaries being connected to the primary to form anauto-transformer, separate load leads extending from the secondaries, astarting coil on said core adjacent the primary coil and located betweenit and one of the secondary coils, separate leads for the starting coilextending outwardly of the transformer, starter switch means connectedto one of the leads of the starting coil for establishing switchingconnections for connecting and disconnecting said starting coil incircuit with one of the secondary coils, and a condenser, said condenserbeing connected in series with the last-mentioned secondary coil.

PAUL BERGER.

REFERENCES CITED The following references are of record in the ile ofthis patent:

UNITED STATES PATENTS Number Name Date Re. 22,712* Gref Jan. 22, 19462,025,471 Osborne Dec. 24, 1935 2,177,883 Foulke Oct. 31, 1939 2,241,261Horn May 6, 1941 2,298,935 Freeman Oct. 13, 1942 2,314,311 Karash Mar.16, 1943 2,332,455 Mauerer Oct. 19, 1943

